The Institute of Electrical and Electronics Engineers (IEEE) standards define beacon transmissions in a number of ways including transmissions from access points (APs) in an infrastructure mode, from wireless local area networks (WLANs) and from clients in “ad hoc” mode. Those skilled in the art will recognize that in the WLAN environment, the “client” is the mobile station or user which utilizes the AP to establish wireless communications with other users or devices. Further, skilled artisans will recognize that the target beacon transmission time (TBTT) in a WLAN is governed by a common network timer called the “timing synchronization function” or the TSF timer and the beacon interval. These two information elements, which are carried in beacons and other management messages, allow for a unique TBTT during each beacon interval that is common to both the AP and all the clients served by that AP. The TBTT represents only a target or expected transmission time for beacons. However, in practice, the beacon transmission may be delayed due to various factors such as interference, loading or the like.
Although the IEEE standards govern system architecture, the beacon transmission methodology by sectorized APs is not well-defined. Those skilled in the art will recognize that a sectorized AP is an AP with multiple directional antennae forming multiple sectors. As described herein, the terms “sectors” and “directional antennae” are used interchangeably. Further, functionalities in a network with multiple tiers of APs and/or clients are even less defined by the standard.
One issue that requires resolution in such networks involves a “neighbor” discovery process at a client that is used to identify and discover sectors of the same AP. This discovery process is not defined by the current standards. Moreover, since beacon transmission times of sectors of the serving AP, where the serving AP is the AP that the client is associated with, are not known by a client or defined by the standards, intelligent scheduling of traffic to and from multiple sectors (for site diversity and efficient make-before-break handoff) cannot be accomplished. Efficient scheduling of traffic reception based on pending traffic notification in beacons is also not possible. In other words, the client may not be able to tell from which antenna and at what time interval to listen for the traffic without a high degree of signaling overhead. Prior art FIG. 1 illustrates such a wireless network 100 where the wireless access point 101 utilizes directional antennas defining sectors 103, 105, 107 and 109. If a client 111 were transitioning from sector 109 to sector 103, it is important that the client 111 receives the beacon traffic from the sector 103 of the access point 101 in a timely manner.
Hence, the client 111 may not be able to schedule uplink traffic efficiently since it may not know when its current sector is sending its beacon or actively receiving traffic. This will result in unnecessary re-transmissions and power drain at a portable client. These problems multiply in complexity when different antennas operate on different frequencies, requiring improved methods of propagating beacons in a wireless local area network.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.